There are many handheld multimeters, which can be interfaced with a computer. However, this arrangement uses two separate apparatus, a computer system and a voltmeter. Therefore, a user should carry a multimeter to do the test, which requires a displaying screen and an electrical measuring device. The selection of a function is controlled from the handheld multimeter and the measured results are displayed on the computer screen. The handheld apparatus should be connected to the rear side of the computer every time it is used. The multimeter interfaced with computers are using serial communication cables. The serial data communications are very slow in transferring data from one device to the other. A parallel data cable can be used, however, this will be costly and bulky.
The aforementioned facts are telling that the multimeters of the prior art are very inconvenient and inefficient to the user in comparison to the computer multimeter of this invention. All functions can be accomplished with only a handheld multimeter. However, the handheld multimeter provides very limited feasibility such as displaying just the measured value. It cannot display a meaningful message nor can it draw an eye-catching illustration.
If a versatile and multi-faceted multimeter is needed, it can be made, but the cost will be expensive. It is the recent trend that engineers, designers, and technicians are using a computer as much as possible for their work because the computer provides unlimited capabilites. The above-listed facts have raised a strong incentive to come up with a new invention of the computer multimeter. This invention is named a PC Multimeter, or Computer Multimeter. The PC Multimeter comprises combination of existing computer circuits and multimeter-specific-circuits.
A method for making computer multimeter by adding multimeter circuits to the existing computer resources in a computer system. In general, a computer can perform many different functions. This invention adds measuring functions to a computer system.
The PC Multimeter comprises input devices such as a keyboard, or disk drives, output devices such as a monitor screen, and internal component devices such as a microprocessor or memory. The above described devices are inherent in the computer. Said multimeter also comprises PPI, buffer/transceiver, A/D converter, timer/counter, and analog measuring circuits. This invention utilizes the existing computer circuitry and devices as part of the PC multimeter as listed above. The other part includes multimeter-specific-circuitry assembled on an I/O expansion board. The I/O board is mounted in an I/O expansion slot inside the computer. Except input/output devices, all circuits and devices are enclosed inside the computer. The only elements of the PC Multimeter extruding outside of the computer are two test leads, which connect the PC Multimeter to the device being tested. Being located inside the computer, the added multimeter-specific-circuits become part of the computer, providing expanded multimeter functions to the computer. The functions of the PC Multimeter are very versatile, and its displaying capability is unlimited, for example, a numerical value, a word message, an illustration, a table, or a graphical representation for a measured magnitude.
This invention provides the ability to have a very fine resolution by adding multiplier circuits for a very small magnitude signal. Since additional multimeter-specific-circuits are added to the existing computer circuits, the buffer and transceiver circuits are inserted between them. The circuits provide high impedance between existing computer circuits and the added circuits preventing the latter from shorting out or loading down the former circuits. The subject multimeter includes the function of a frequency counter in addition to the most common voltmeter, current meter, ohmmeter, and waveform meter. The edge shaping circuit converts any incoming periodic signal into a rectangular wave which is easier to trigger the frequency counter. The counter counts the input frequency and couples the measured result to the microprocessor through the interfacing circuits, which includes buffer/transceiver and programmable peripheral interface circuits.
For the analog measuring circuits, a key from the keyboard initiates a function and the microprocessor controls the pertinent switch. The appropriate range is automatically selected by the microprocessor under a program control. Five function switches are utilized, one for each function. Those switches are high current and high voltage electronic switches. The range switches are typical bilateral electronic switches. Even though the computer multimeter of this invention includes only five functions, any number of functions can be added to it, because today""s microprocessor equipped within a personal computer has unlimited control capability.